The present invention relates to an optical pickup and more particularly to an optical pickup to be used for a disk apparatus (for example, a DVD recorder or a DVD player).
The related art of an optical pickup has been described in JP-A-2004-22034. An example will be described with reference to FIGS. 4 to 7. As shown in FIGS. 4 and 5, a metallic slide base 3 is engaged with a pair of left and right guide rails 2 in a radial direction of a disk D disposed in a housing 1 so as to freely carry out a reciprocation a and b, and a light receiving device PD1 for reading and a light receiving device PD2 for light amount detection which include a photodiode and a laser beam source LD which includes a laser diode are disposed on an erected frame 4 formed integrally with the slide base 3, and furthermore, a polarizing beam splitter PBS, a half mirror HM and an objective lens OL, and a diffraction grating GRT are disposed in the erected frame 4.
An information reading procedure will be described below. A laser beam is emitted from the laser beam source LD through the diffraction grating GRT, the polarizing beam splitter PBS, the half mirror HM and the objective lens OL onto the disk D to be rotated at a high speed, and the reflected light is transmitted through the objective lens OL, the half mirror HM and the polarizing beam splitter PBS and is received by the light receiving device PD1, thereby reading information recorded on the disk D. Moreover, an amount of the light emitted from the laser beam source LD is detected by the light receiving device PD2 and the amount of the light emitted from the laser beam source LD is regulated by a controller of the disk device based on the detection signal.
As shown in FIGS. 6A, 6B, 6C and 7, a grating hole 6 and a pair of concave grooves 7 extended in opposite directions to each other from an outer peripheral edge of the grating hole 6 are formed on a reference end face 4a of the erected frame 4, and the diffraction grating GRT is disposed in the grating hole 6, and there is provided a pressing spring 8 including a ring portion 8a disposed in the grating hole 6 and abutting on the diffraction grating GRT and a pair of arm portions 8b extended in opposite directions to each other from an outer peripheral edge of the ring portion 8a and inserted in the concave grooves 7, and the pressing spring 8 has an overall length r which is small, that is, approximately 8 mm.
The laser beam source LD is attached to the reference end face 4a through a spring plate frame 9 and a holder 10, and the spring plate frame 9 includes a bottom plate 9a to abut on the reference end face 4a and a pair of side plates 9b and 9c which are bent almost perpendicularly from both side edges of the bottom plate 9a, and a laser hole 11 is provided on a center of the bottom plate 9a opposite to the grating hole 6 and an almost U-shaped slit 12 is formed on both ends of the bottom plate 9a so that a residual tongue piece 13 is raised. A communicating hole 15 is provided between the laser hole 11 and each slit 12 in the bottom plate 9a opposite to a through hole 14 of the reference end face 4a, and both ends of the bottom plate 9a are fastened to the reference end face 4a with an adhesive 16 formed of an ultraviolet curing adhesive (or a thermosetting adhesive) so that tips of both arm portions 8b of the pressing spring 8 are pressed by the bottom plate 9a (see FIG. 6B). Consequently, the ring portion 8a is pushed against the diffraction grating GRT by an elastic force which is generated. Thus, it is possible to prevent the diffraction grating GRT from being rotated unexpectedly.
As shown in FIG. 6C, a slot 17 is formed on each of the side plates 9b and 9c and a projection 10a provided on the holder 10 is fitted in the slot 17 so that the laser beam source LD is engaged with the spring plate frame 9 through the holder 10. In FIG. 6C, 18 denotes an operating hole for communicating with the grating hole 6 through the erected frame 4. An operating rod 19 is caused to come in contact with an outer peripheral surface of the diffraction grating GRT through the operating hole 18 to carry out an operation. Consequently, the diffraction grating GRT is rotated to disperse the laser beam as desired.
Description will be given to an assembling procedure. The diffraction grating GRT is inserted into the grating hole 6 in a state in which the reference end face 4a is turned upward, and the ring portion 8a of the pressing spring 8 is then inserted into the grating hole 6, and furthermore, each of the arm portions 8b of the pressing spring 8 is inserted into the concave groove 7 and the bottom plate 9a of the spring plate frame 9 is mounted on the reference end face 4a. The spring plate frame 9 is moved horizontally along the reference end face 4a to finely adjust a directivity of the laser beam emitted from the laser beam source LD, and the spring plate frame 9 is then fastened to the reference end face 4a with the adhesive 16.
With the structure of the related art, the small and light pressing spring 8 is simply put slightly in the grating hole 6. During an assembling work, therefore, a tool hits on the slide base 3 so that the pressing spring 8 jumps out of the grating hole 6 by a shock and is thus lost, for example. In some cases in which the spring plate frame 9 is moved horizontally along the reference end face 4a, moreover, a laser hole 11 of the spring plate frame 9 is caught on a tip of the arm portion 8b of the pressing spring 8 so that the position of the pressing spring 8 is shifted. For this reason, an efficient assembling work is inhibited.
Furthermore, both of the arm portions 8b of the pressing spring 8 abut on the bottom plate 9a of the spring plate frame 9. Therefore, the elastic force of the pressing spring 8 is applied to the bottom plate 9a of the spring plate frame 9 in addition to the contraction and expansion of the adhesive 16 which is caused by a change in an environmental temperature. Consequently, the position of the spring plate frame 9 is shifted so that the directivity of the laser beam emitted from the laser beam source LD might be subtly disordered.